In recent years, organic EL (electroluminescence) devices have been drawing attention as display devices such as mobile phone display panels or flat-screen televisions. In particular, top-emission type organic EL devices, in which light is emitted from the side opposite to a driving circuit board, are suitable for achieving high luminance and high definition, because the top-emission type devices can ensure a high aperture ratio with no restriction by light-blocking objects such as TFT (Thin Film Transistor) and a wiring, as compared with bottom-emission type organic EL devices, in which light is emitted from the side having a driving circuit board. In such top-emission type organic EL devices, it is the mainstream to use a structure in which a buffer layer made of ITO, IZO, AZO, MoO3 or V2O5 is directly formed on the surface of an anode (reflective film) made of an Al alloy or an Ag alloy. In this way, the currently mainstream buffer layers contain oxygen, which is used as an oxide to constitute a buffer layer, so as to achieve a balance between work function and high transmission rate due to wide gap. In these oxide buffer layers, it is necessary to heighten the work function by subjecting the surface of the buffer layer to oxygen-plasma treatment, ozone treatment or the like so as to forcibly dope with oxygen.
However, the oxide buffer layer forcibly doped with oxygen causes a phenomenon in which oxygen gradually leaks out to lower the work function. Moreover, it is known that organic materials used in organic EL devices, such as a hole injection layer (2-TNATA), are sensitive to oxygen and water, under the presence of which organic layer properties deteriorate.
There is also known a technique for forming an insulating amorphous carbon film on an anode ITO film. For example, a technique is known in which the surface of an anode is flattened by forming an amorphous carbon layer on an ITO film to improve light emitting efficiency and light emitting stability (see Patent Literature 1). In this technique, the formation of the amorphous carbon film is conducted by sputtering during which a mixture gas of hydrogen and argon gas (with a hydrogen proportion of 5%) is flowed. In addition, there is also known a technique in which an insulating amorphous carbon film having a specific resistance of higher than 100 Ω·cm is provided on an anode to improve hole injection efficiency between the anode provided with the carbon film and an organic light emitting layer (see Patent Literature 2).
On the other hand, there is also known a technique in which a diamond-like carbon film electrode having a high electrical conductivity is formed by RF-PECVD on an anode such as an ITO film (see Patent Literature 3). However, this technique requires many steps in that it is necessary to dope the diamond-like carbon film with impurities for providing electrical conductivity as well as to terminate the surface of the diamond-like carbon film with fluorine or the like for heightening the work function by conducting an RF plasma treatment during which a gas such as CF4 is introduced. Moreover, the diamond-like carbon film produced by this technique contains impurities or the like at a meaningful level, raising a concern with negative effects such that the impurities are diffused into the organic EL layer which is in direct contact with the diamond-like carbon film.
In the meantime, a structure having an organic EL layer interposed between electrode materials is advantageous in terms of mass productivity and cost competitiveness of organic EL panels, while the decrease in cathode conductance becomes unignorable as the light emitting part becomes larger. This causes the necessity to increase the cathode conductance by connecting an auxiliary wiring to the cathode. An example of such conventional organic EL devices is shown in FIGS. 13 and 14. FIG. 13 shows a top view of the organic EL device, while FIG. 14 shows a cross-sectional view taken along line A-A′-B of FIG. 13 (i.e., a combined view of the cross-sectional view taken along line A-A′ and that along line A′-B). As shown in FIG. 14, the organic EL device 100 has, on a driving circuit board 101, an anode (reflective film) 102 having a laminated structure in which a Mo/Ag or Ag alloy and a buffer layer such as ITO are laminated in order, an organic EL layer 103, and a cathode 104 made of a Mg—Ag alloy, all of which are laminated in order. In addition, at a location separated from the organic EL layer 103 by a flattening film 105, a downwardly-bent part of the cathode 104 is in direct contact with an auxiliary wiring 106 having a laminated structure in which a Mo/Al or Al alloy and a buffer layer made of a high-melting-point metal such as Mo are laminated in order. As shown in FIG. 13, the auxiliary wiring 106 is provided so as to be vertical and parallel to a gate wiring 107 and a source wiring 108 as well as to be parallel to the outer edge of the organic EL layer 103. This configuration of the auxiliary wiring 106 enables electrons to flow uniformly over the entire area of the organic EL layer 103. For such structure, a further improvement in productivity is desired, since the different laminated structures of the anode (reflective film) 102 and the auxiliary wiring 106 increase the types of the materials, complicate the process, and increase the number of the process steps.